Conventionally, in an auger type ice making machine, as disclosed in, for example, Japanese Utility Model Publication No. 63-10453, a pair of normally open type float switches are provided at the top and bottom of a water tank, so that when the lower float switch is opened, water to be formed into ice is supplied into the water tank from a water source by opening of a solenoid water valve, an ice making operation starts when both float switches are closed in accordance with an increase of water in the water tank to a given quantity to form the water from the water tank into ice crystals and move the ice crystals out of an evaporator housing with an auger to sequentially store them as pieces of hard ice in a storage bin, the same water supply to the water tank and the ice making operation are repeated after the lower float switch is opened in accordance with a decrease of water in the water tank.
With the above structure, as long as both float switches properly function, the ice making operation is automatically ensured when suspension of water supply occurs and water supply is then recovered. When suspension of water supply occurs, however, the lower float switch is opened, holding the solenoid water valve open. For this reason, the longer the suspension of water supply continues, the greater the wasteful power consumption becomes to keep the solenoid water valve open.
Meanwhile, there may be such malfunctions that the individual float switches are disabled to be opened or closed due to dust entering together with water in the water tank or melting of the contacts of each float switch caused by an excessive current flowing therethrough. In those malfunctions, if closing of the upper float switch is not possible, this upper float switch cannot be closed when water in the water tank increases to a given quantity. The solenoid water valve cannot therefore be closed, so that supply of water in the water tank from the water source will continue even after the water tank is filled with water. As a result, water in the water tank is discharged wastefully through an overflow pipe and the place where the ice making machine is set is flooded with water.
If opening of the upper float switch is not possible, this upper float switch cannot be opened even when water in the water tank is insufficient. The solenoid water valve cannot therefore be opened, so that ice making operation will continue even when there is insufficient water in the water tank or insufficient water in the evaporator housing, resulting in over freezing in the evaporator housing. As a result, the amount of circulation of a fluid refrigerant from the evaporator in the evaporator housing to the compressor increases, damaging the components of the compressor or the over freezing in the evaporator housing acts as an over load to a driving mechanism through the auger, damaging the components of this driving mechanism.
If closing of the lower float switch is disabled, this lower float switch cannot be closed even though the level of water in the water tank is kept proper between the locations of the upper and lower float switches. Consequently, water supply to the water tank from the water source via the solenoid water valve starts even though the proper amount of water is remaining in the water tank. Accordingly, in this case water is not used for ice making to sufficiently reduce the water for one cycle retained in the water tank, dropping the ratio of use of the water and shortening the service life of the solenoid water valve due to the increased frequency of opening/closing actions.
If opening of the lower float switch is disabled, this lower float switch cannot be opened even though there is insufficient water in the water tank. Therefore, ice making operation will continue even when there is insufficient water in the evaporator housing, resulting in over freezing in the evaporator housing. This causes substantially the same shortcoming as arising in the case where opening of the upper float switch is disabled.
Further, with the above-described structure, if a refrigerant leaks from a pipe in a refrigeration circuit having an evaporator or compressor, the evaporator does not show sufficient cooling performance due to an insufficient refrigerant, making the ice making operation unnecessarily longer. In some cases, the refrigeration circuit becomes a vacuum-operating state due to the refrigerant leakage, so that outside air is sucked inside, causing a critical damage on the components of the circuit.